Journal
BLOOD
Volume 102, Issue 10, Pages 3658-3664Publisher
AMER SOC HEMATOLOGY
DOI: 10.1182/blood-2003-06-1888
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Funding
- NHLBI NIH HHS [HL-44612, R24 HL063098] Funding Source: Medline
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Platelet adhesion at sites of vascular injury is mediated, in part, by interaction of the platelet plasma membrane glycoprotein (GP) Ib/V/IX complex with von Willebrand Factor (VWF) presented on collagen-exposed surfaces. Recent studies indicate that GPIb/V/IX may be functionally coupled with the Fc receptory gamma (FcRgamma)-chain, which, by virtue of its cytoplasmic immunoreceptor tyrosine-based activation motif, sends activation signals into the cell. Platelet endothelial cell adhesion molecule-1 (PECAM-1) is an inhibitory receptor that has previously been shown to negatively regulate platelet responses to collagen, which transduces activation signals via the GPVI/FcRgamma-chain complex. To determine whether PECAM-1 might similarly regulate signals emanating from GPIb/FcRgamma, we compared activation and aggregation responses to VWF of PECAM-1-positive and PECAM-1-deficient murine platelets. PECAM-1 and the FcR-gamma-chain became rapidly tyrosine phosphorylated in platelets following botrocetin-induced VWF binding, but FcRgamma-chain tyrosine phosphorylation was delayed in PECAM-1-positive, versus PECAM-1-deficient, platelets. PECAM-1-deficient platelets were hyperaggregable to VWF, exhibited enhanced spreading and, under conditions of arterial flow, formed markedly larger thrombi on immobilized VWF than did wild-type platelets. Taken together, these data support the notion that engagement of the GPIb complex, in addition to sending activation signals, also initiates a negative feedback loop involving PECAM-1 that controls the rate and extent of platelet activation.
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